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For decades, nutritionists and dietitians have disparaged the very-low-carbohydrate Atkins diet because it is high in saturated fat and because its purported benefits had not been tested in formal studies. According to the conventional wisdom, a diet low in fat and high in starch reduces the risks for heart disease and cancer and promotes weight loss. However, these claims do not have solid evidence to support them. In large prospective studies, total fat intake does not predict cancer risk (1). In addition, dietary fat per se does not predict the risk for coronary heart disease in ecologic and prospective studies or clinical trials (2, 3); however, intake of specific fatty acids is important. Moreover, high-carbohydrate diets, which reduce high-density lipoprotein (HDL) cholesterol and raise triglyceride levels, exacerbate the metabolic manifestations of the insulin resistance syndrome (4). The primary remaining justification for high-starch diets has been weight control, but even this rationale is on shaky ground (5, 6). Meta-analyses of studies that mostly lasted 6 months or less suggest a small benefit for low-fat diets (typically 20% to 25% of energy) compared with moderate-fat diets (usually 35% to 40% of energy) (5). However, patients on low-fat diets typically regain lost weight. Two meta-analyses of studies lasting 1 year or more found no sustained reduction in weight; the weighted mean difference in weight change (low-fat diet group minus control group) was −0.25 kg in one analysis (7) and +3.7 kg in another (8), even though the low-fat groups had more intensive interventions, which would create bias in their favor.